1. Field of the Invention
This invention relates to an optical semiconductor apparatus with an optical semiconductor chip built in a metal package.
2. Background Art
In a typical configuration of an optical semiconductor apparatus used for optical transmission/reception, an optical semiconductor chip, such as a semiconductor laser, light emitting diode, and photodiode, is placed in a metal package, and a lead for externally extracting an electrical signal is connected to the optical semiconductor chip by a metal wire in the metal package. As a metal package for an optical semiconductor apparatus, a TO (transistor outline) package is widely used, which is easily connected to an optical fiber and highly versatile.
On the other hand, with the recent increase in demand for Internet communication, optical fiber communication apparatuses have become faster. Optical semiconductor apparatuses also require a technique for housing an optical semiconductor chip and a multifunctional semiconductor component in a single package in order to prevent degradation in S/N ratio due to increased speed and provide a high-performance optical semiconductor device.
For instance, Patent Document 1 discloses an optical receiver with a photodiode and a preamplifier housed in a TO package. Patent Documents 2 and 3 disclose a technique for housing a plurality of semiconductor components in a single package using an insulative flexible substrate.
However, the conventional technique disclosed in the above Patent Documents 2 and 3 is a technique applied to a large package, which is distinct from the package used for optical semiconductor apparatuses, and the technique is different from this invention in objects and problems. In the following, the problems to be solved by the invention are described with reference to the drawings.
FIG. 1 is a schematic view illustrating the connection of an optical semiconductor apparatus 1 based on a TO package to an optical fiber 40. The TO package is composed of a base 3 and a cap 2. The cap 2 is provided with a lens 5 for optical transmission/reception to/from the optical fiber 40. An optical semiconductor chip is placed inside the TO package and electrically connected to a lead 4 inserted through the base 3 from outside to inside.
FIG. 2 is a schematic view showing the A-A cross section (see FIG. 1) of an optical semiconductor apparatus for receiving an optical signal and converting it into an electrical signal. A photodiode 6 bonded onto a submount 7 is placed on a component placement surface 3b of the inside of the base 3. A metal interconnect is provided on the surface of the submount 7 and electrically connected to the photodiode 6. Furthermore, a semiconductor component 8, such as a preamplifier and TIA (transimpedance amplifier), and a passive component 9, such as a capacitor and resistor, are placed on the component placement surface 3b. 
The photodiode 6 bonded onto the submount 7 is connected to the lead 4 by a metal wire 10 through the semiconductor component 8 or the passive component 9. Light injected from the optical fiber 40 into the photodiode 6 is converted into an electrical signal by the photodiode 6, amplified by the semiconductor component 8, and externally extracted by the lead 4. The lead 4 is inserted into an opening 4b provided through the base 3 from outside to the component placement surface 3b. The lead 4 is insulated from the base 3 by an insulative glass sintered body 12.
FIG. 3 is a schematic view showing the component layout of the TO package shown in FIG. 1. Five leads 4, including the leads not shown in FIGS. 1 and 2, are placed in the component placement surface 3b of the base 3. Five openings 4b provided in the base 3 are each sealed with the lead 4 and the glass sintered body 12 surrounding the lead 4. Furthermore, the submount 7 with the photodiode 6 bonded thereto, the semiconductor component 8, and the passive component 9 are placed and connected by metal wires 10.
In order to allow the above optical semiconductor apparatus to receive a fast optical signal, it is useful to replace the semiconductor component 8 by a multifunctional semiconductor component to eliminate loss due to transmission of electrical signals between a plurality of functional devices. When a multifunctional semiconductor component is housed in a TO package, it is necessary to place a semiconductor component having a large chip size due to its multifunctionality, and a newly required passive component. Thus, one problem is to obtain space for placing these components in the limited space of the component placement surface 3b of the base 3.
In a small TO package, the area of the openings 4b sealed with the glass sintered body 12 accounts for a large proportion of the component placement surface 3b. On the other hand, no component can be placed on the glass sintered body 12. Hence, the effective space for placing components is limited. Furthermore, if the number of leads 4 is increased to provide new input terminals in order to house a multifunctional semiconductor component, the space is further decreased.
Furthermore, increase in the number of housed components complicates interconnection by metal wires. Thus, component layout without intersection between metal wires is difficult, which is another problem.    Patent Document 1: US 2004/0264980 A1    Patent Document 2: JP-A-9-232500    Patent Document 3: JP-A-10-4510